In the prior art, of which I am aware, portable electric drills and other power tools traditionally employ a chuck or collet to securely retain the drill bit or other tool element therein and facilitate its advancement into the workpiece. In portable electric drills intended for consumer usage, a geared chuck and conventional chuck key are employed. For drills intended for heavy-duty industrial applications, the chuck may be of the conventional geared type or else of the keyless type. In both cases, the chucks are operated manually.
Manually-operated chucks and collets have also been used to hold various tools and workpieces in the machine arts. One example is the cam-operated chuck disclosed in U.S. Pat. No. 2,735,687. In that patent, a plurality of balls cooperate with a cam formed on the collet, and the collet opens or closes in response to the direction in which a hand wheel is turned.
Besides the manually-operated chucks, the prior art has also resorted to air-operated chucks for lathes and other machine tools. This general concept has also been applied to a portable pneumatic tool as disclosed in U.S. Pat. No. 3,712,386. In that patent, the pressure of the compressed air selectively operates a reciprocatory spring-loaded piston to open the gripping jaws of the tool collet, thereby providing a quick-release feature. Alternately, as disclosed in U.S. Pat. No. 3,724,563, the pivoted lever for throttle control of a portable pneumatic tool is moved in a direction opposite to its normal mode of operation to actuate a mechanical linkage to open the tool collet.
In drills used for surgical or orthopedic purposes, a cannulated spindle has a through bore for receiving a Kirchner pin, usually referred to in the art as a "K wire". The K-wire is retained in a collet or chuck mounted on the forward end of the spindle. In some commercial embodiments, a pivoted release lever facilitates insertion of the K-wire (and its subsequent advancement relative to the drill) without the use of additional keys and accessories. The lever has a bifurcated portion engaging a spring-loaded slidable collar that actuates a mechanism to open the chuck. The remaining portion of the lever is bent around the trigger, forwardly thereof and providing a guard therefor, and terminates in a depending portion. One finger on the doctor's hand engages the trigger, while the doctor's remaining fingers are wrapped around the depending portion of the lever during operation of the tool. This is somewhat awkward and inconvenient. Moreover, in order to preclude inadvertent release of the collet during a surgical procedure, the spring pressure must of necessity be relatively heavy. As a result, whenever release of the collet is desired, a strong force must be exerted on the lever by the doctor. Repeated opening and closing of the collet can thus be tiresome during an extended surgical procedure.
In another commercial embodiment, a surgical tool is equipped with a pneumatic collet controlled by a trigger projecting forwardly of the pistol-grip handle of the tool. When the trigger is depressed partially, the collet closes; to securely retain the K-wire therein; and when the trigger is depressed fully, the tool is energized to drive the wire. While facilitating insertion and removal of the K-wire from the collet, the operator must continually depress the trigger by a predetermined amount to maintain the collet closed and to preclude inadvertent release of the K-wire. This detracts from the doctor's concentration and interferes with close surgical procedures in an operating room or clinic. Moreover, if the trigger would be completely released and the tool subsequently tilted or inverted, the K-wire could fall out of the tool and would no longer be usable because of hygienic considerations.
A possible solution is the surgical drill disclosed in U.S. Pat. No. 3,718,340. In that patent, a pivoted lever is mounted on the side of the drill. Actuation of the lever initiates a mechanical linkage to ultimately open the gripping jaws of the collet to release the K-wire. However, not only does actuation of the lever require a partial release of the doctor's hand grip, but of necessity, the drill is oriented for "right handed" usage. Moreover, a heavy spring pressure is required to maintain the collet in its closed position and preclude inadvertent release of the K-wire. To overcome this heavy spring pressure, the lever actuates the collet through a mechanical linkage. This mechanical linkage includes a pivoted yoke, a spring-loaded slide, a plurality of cam levers, respective push rods, and a hollow cone to actuate the gripping jaws of the collet. This linkage is unduly complicated, hence expensive and potentially unreliable.
Thus, the collets and chucks for surgical drills and other power tools, resorted to in the prior art, have had certain inherent disadvantages or deficiencies; and despite the highly-deveLoped state of the art, a practical, economical and reliable solution to a problem of long standing has heretofore eluded the designers and researchers in the field.